Manufacturing process for semiconductor device, photomask, and manufacturing apparatus for semiconductor device

ABSTRACT

Provided are a manufacturing process for a semiconductor device capable of transferring a pattern corrected with respect of optical distortion of an exposure apparatus, a mask, and a manufacturing apparatus for a semiconductor device.  
     The manufacturing process, regarding optical distortion of said exposure apparatus as a variation in reduction rate of a transferred pattern in each of regions, includes: a first step transferring a fundamental pattern formed on a reference photomask for measuring the optical distortion to measure a size of a transferred pattern in a corresponding one of regions; and a second step of, based on a result obtained in said first step, forming a corrected photomask having a pattern corrected in said corresponding one of regions with respect to said optical distortion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a manufacturing process for asemiconductor device by means of which improvements are achieved onaccuracy and uniformity of a size of a transferred pattern in a patterntransfer step of the manufacturing process for a semiconductor device bysuppressing optical distortion of an exposure apparatus, a photomask anda manufacturing apparatus for a semiconductor device.

[0003] 2. Description of the Background Art

[0004] In an exposure apparatus used in manufacturing a semiconductordevice, light radiated from a light source is transmitted throughpatterns on a photomask to be projected on a wafer surface to make animage. In FIGS. 28 and 29, shown are prior art photomasks formed bymeans of a prior art method. In FIG. 28, arranged are rectangularpatterns 113 a of the same shape having a side a in length in a uniformdistribution on a photomask 103. Furthermore, in FIG. 29, formed is asingle pattern 113 b having a constant width L along a bending shape inphotomask 103. A photoactive positive or negative photo resist isapplied on a semiconductor wafer in advance. When a positive photoresistis employed, a part of the photoresist on which light through aphotomask is irradiated is removed in a following developing step, whilea non-irradiated part of the photoresist on which the light doesn'tirradiate remains in the following developing step. With such a processadopted, a pattern on the photomask is transferred on the wafer as apattern of photo resist. By using the pattern of the photoresist,etching and impurity implantation are performed to manufacture asemiconductor device.

[0005] A photomask is manufactured such that as shown in FIG. 28,patterns of the same size are arranged in a repeated arrangementperiodical arrangement) and the same patterns are distributed in auniform manner with respect to a size in each of regions all over thesurface of the mask regardless of locality of a region to increaseuniformity in terms of size of devices. Moreover, there is also includeda step in which a non-repeated pattern (non-periodical pattern) as shownin FIG. 29 is transferred. The pattern with no repetition is alsotransferred by means of a transfer apparatus such that no variation insize occurs. Hence, each optical systems such as lenses of exposureapparatuses are designed and manufactured such that a pattern istransferred with uniformity.

[0006] Distortion in an optical system of an exposure apparatus is,however, difficult to be perfectly eliminated and in addition,characteristics of the distortion are different in each exposureapparatus. For this reason, a pattern on a photomask is not necessarilytransferred in a faithful manner. As a result, a transferred resistpattern is affected by optical distortion specific to each exposureapparatus, resulting in a variation in performance of a semiconductordevice.

[0007] In order to solve such a problem, a proposal has been made on aphotomask to correct optical distortion in an exposure apparatus (seeJapanese Patent Laying-Open No. 60-167328 and Japanese PatentLaying-Open No. 8-95229). By use of such a photomask corrected withrespect to optical distortion, a variation in performance of asemiconductor device is alleviated. Correction methods for opticaldistortion disclosed in the above described publications are, however,to correct positional displacements of points on a photomask, whereinobjects for the correction are a direction of a displacement and adistance thereof. Therefore, there has remained a problem in that thecorrection of optical distortion is complex and that no recognizableimprovement can be achieved without the correction with very highaccuracy. Since in a manufacturing process of a semiconductor device, atremendous number of photomasks are employed, even only photomasks usedin manufacturing steps which affect characteristics of the semiconductordevice are difficult to be corrected in advance when depending on toocomplex a correction method. Hence, in company with progress inmicrofabrication of a semiconductor device, there has been built up ademand for a manufacturing process for a semiconductor device capable ofobtaining an exposure-transferred pattern with high accuracy in a simpleand convenient manner.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide amanufacturing process for a semiconductor device capable of correctingoptical distortion of an exposure apparatus in simple and convenientmanner, a mask for use in the manufacturing process, and a manufacturingapparatus provided with the mask for a semiconductor device.

[0009] A manufacturing process for a semiconductor device of the presentinvention is a manufacturing process for a semiconductor deviceincluding a step of transferring a pattern on a photomask onto asemiconductor wafer by means of an exposure apparatus. The manufacturingprocess regards optical distortion of an exposure apparatus as avariation in reduction rate of a transferred pattern in each of regionsof a photomask and includes: a first step of transferring a fundamentalpattern formed on a reference photomask for measuring the opticaldistortion to measure a size of the transferred pattern in acorresponding one of regions; and a second step of, based on a resultobtained in the first step, forming a corrected photomask having apattern corrected in the corresponding one of regions with respect tothe optical distortion.

[0010] According to such a constitution, an optical distortion can beobtained as a size of a pattern in each region on a photomask, or a rateof a size of a transferred pattern in a corresponding region and a sizeof a pattern on the photomask. The size and size rate can be obtainedwith ease, and furthermore, a corrected photomask can be fabricatedbased on the size or size rate in a simple and convenient manner. Forthis reason, a tremendous number of photomasks for use in manufacturingsteps to affect characteristics of a semiconductor device can bereplaced with respective corrected photomasks in a simple and convenientmanner. Consequently, not only can a variation in a transferred patternin each of exposure apparatuses can be restricted, but a dimensionalvariation in each of portions in a semiconductor device caused byoptical distortion, which differs between exposure apparatuses, can besuppressed, such that sizes of portions in a semiconductor device formedthrough a different exposure apparatus can be all uniform. As a result,miniaturized semiconductor devices with high reliability can be providedwith a high manufacturing yield. Note that optical distortion appears asa variation in a magnification rate or reduction rate in each region;therefore, the above described fundamental patterns are desirablyprovided across all regions of a reference photomask.

[0011] In the manufacturing process for a semiconductor device of thepresent invention, a fundamental pattern on the reference photomask is,for example, a plurality of unit patterns of the same shape arranged onthe reference photomask.

[0012] By providing a reference photomask having unit patterns arrangedthereon as described above, the area of a photomask is divided intoregions including each unit pattern and a magnification rate orreduction rate can be obtained in each region. In a corrected photomask,a pattern size is corrected in each region based on a magnification rateor reduction rate for the region. This correction is performed such thata product of a magnification rate or reduction rate in each region and apattern size in a corresponding region of a corrected photomask is thesame as each other in any of all the regions regardless of particularityof a region. By use of the corrected photomask, when patterns of thesame shape are intended to be disposed, for example, in a repeatedarrangement (periodical arrangement) in a transferred pattern, the samepatterns can be obtained in the respective regions as intended, in thetransferred pattern.

[0013] In the manufacturing process of a semiconductor device of thepresent invention, a fundamental pattern on the reference photomask maybe, for example, a non-periodical pattern with no periodicity formed onthe reference photomask.

[0014] In manufacture of a semiconductor device, there are many caseswhere a single pattern with no periodicity is transferred and such anon-periodical pattern is necessary to be corrected with respect to avariation in size due to optical distortion. In a case of thenon-periodical pattern as well, correction of a variation in size iseffected by correcting a variation in reduction rate of each regionsimilar to the case of a periodical pattern. As a result, a sizeaccuracy in a pattern is improved and a variation in size betweensemiconductor devices processed by respective different exposureapparatuses can be restricted.

[0015] In the manufacturing process for a semiconductor device of thepresent invention, the first step desirably includes: for example, astep of obtaining a reduction rate which is a rate between a size of thetransferred fundamental pattern and a size of the fundamental pattern onthe reference photomask in each of regions of the reference photomask.

[0016] By obtaining a reduction rate in each of the regions, a correctedphotomask can be manufactured with simplicity and convenience. When itis intended that the same patterns are provided in respective regions ina transferred pattern, patterns on a corrected photomask have only to beformed such that a size of each of the respected patterns on thecorrected photomask is in inverse proportion to a reduction rate of acorresponding region.

[0017] In the manufacturing process for a semiconductor device of thepresent invention, it is desirable that in the second step, for example,a size of a pattern in each of the regions of the corrected photomask isdesirably formed such that a corrected reduction rate which is a ratebetween a size of a corrected, transferred pattern that is a transferredpattern of a pattern of the corrected photomask and a size of a patternon the photomask prior to the correction in each of the regions is thesame throughout all the regions regardless of each locality.

[0018] According to the above described constitution, optical distortionof an exposure apparatus is eliminated and a transferred pattern asintended can be obtained. For this reason, even when a transfer step isperformed in a different exposure apparatus, photoresist patterns of thesame size or the like are formed on a semiconductor substrate; andetching, impurity implantation and others can be performed based on thephotoresist patterns of the same size. As a result, semiconductordevices with a high manufacturing yield, high reliability and highperformance can be provided with simplicity and convenience.

[0019] In the manufacturing process for a semiconductor device, in thesecond step, for example, a size of a pattern in each of the regions ofthe corrected photomask is desirably formed such that a product of apattern correction rate which is a rate between a size of a pattern in aregion on the corrected photomask and a size of a pattern in acorresponding region of the photomask prior to the correction and areduction rate in the region is the same regardless of which of all theregions the region belongs to.

[0020] The photomask prior to the correction is a photomask in a casewhere it is assumed that no optical distortion is present in an exposureapparatus and may be either existent or imaginary. By forming a patternon a corrected photomask as described above, when the correctedphotomask is used in the exposure apparatus, the optical distortion canbe eliminated in terms of size. As a result, patterns which have beentransferred in different ways in respective different exposureapparatuses can be transferred in a similar way as each other regardlessof an exposure apparatus; therefore, high reliability semiconductordevices can be manufactured with a high manufacturing yield. Note thatthe above described pattern may be either a pattern set constituted ofthe same pattern repeatedly arranged in each of regions in a similar wayor a pattern with no periodicity (non-periodical pattern) arrangedacross regions.

[0021] In the manufacturing process for a semiconductor device of thepresent invention, it is desirable that in the second step, for example,a pattern of a prescribed portion of the semiconductor device arearranged in each of the regions of the corrected photomask in a similarway, and a size of a pattern in each of the regions of the prescribedportion of the semiconductor device is determined such that a product ofa size of a pattern of the prescribed portion of the semiconductordevice in a region on the corrected photomask and a reduction rate inthe region is the same all over the regions regardless of which of allthe regions the region belongs to.

[0022] In a case where a pattern set is constituted of patterns of thesame shape arranged in respective regions, a photomask prior tocorrection is not necessary to be referred to but a corrected photomaskcan be manufactured according to the above described constitution. Byusing the corrected photomask in the exposure apparatus, opticaldistortion can be eliminated in terms of size, thereby enablingmanufacturing a high reliability semiconductor device with a high yield.

[0023] In the manufacturing method for a semiconductor device of thepresent invention, it is allowed that the second step includes aphotomask manufacturing process and a pattern of the corrected photomaskmay be corrected in terms of size by adjusting at least one of a writingbeam diameter and a writing dose with respect to a position of thecorrected photomask in a resist writing step of the photomaskmanufacturing process.

[0024] In a case where a positive resist is used, a resist-lackingsection occurs covering a large area if a writing beam diameter and awriting dose is large. That is, since an area of a resist-lackingsection is in proportion to a writing beam diameter or a writing dose, asize of a pattern in each region can be adjusted by controlling suchfactors. The adjustment of a size in this case is not so large as toproduce a change in shape of a pattern, but only at a subtle level ofthe order to be perceptible by an expertise, which is achieved bycontrolling at least one of a writing beam diameter or a writing dose asdescribed above. Hence, by controlling the factors in a proper manner,an appropriate correction can be effected in a simple and convenientmanner with good efficiency.

[0025] In the manufacturing process for a semiconductor device of thepresent invention, it is allowed that the second step includes aphotomask manufacturing process and a pattern on the corrected photomaskis corrected in terms of-a size by adjusting a way of supply of adeveloper in a resist developing step of the photomask manufacturingprocess.

[0026] The adjustment can also be performed in a resist developing step.A developing reaction is accelerated at a writing site supplied with afresh, unused developer and thereby, resist removal progresses ahead ofthe other sites to a larger extent there. For this reason, by adjustinga position and a direction of a nozzle; a residence time at each site ofa nozzle, if movable; in addition, a discharge amount of a developer;and others, formation of a corrected pattern with a desired pattern sizedistribution is effected. Since the optical distortion, in many cases,differs at a degree thereof in each of regions partitionedconcentrically, formation of a pattern in each of the regions may besufficiently controlled, in many cases, if the photomask is separatedinto central and peripheral regions and an intermediate regiontherebetween. Note that correction of an area of a resist-lackingsection can also be effected on an area of a writing site of the samemagnitude.

[0027] In the manufacturing process of a semiconductor device of thepresent invention, it is also allowed that the second step includes aphotomask manufacturing process and a pattern on the corrected photomaskis corrected in terms of size by adjusting a way of supply of an etchingliquid in a wet etching step for a Cr film in the photomaskmanufacturing process.

[0028] The way of supply of a developer applies to a way of supply ofthe etching liquid in the wet etching of a Cr film without any changetherein. Hence, a size of a Cr film-lacking section can be correctedeven when an area of a resist-lacking section is the same.

[0029] In the manufacturing process of a semiconductor device of thepresent invention, it is also allowed that the second step includes aphotomask manufacturing process and a pattern of the corrected photomaskis corrected in terms of size by adjusting a strength of a magneticfield in a dry etching step for a Cr film of the photomask manufacturingprocess.

[0030] By adjusting a strength of a magnetic field, a flow of a plasmagas, which is constituted of an etching gas, can be controlled. As aresult, a desired, corrected photomask can be obtained by adjusting anetching rate in each of central and peripheral regions and anintermediate region therebetween.

[0031] In the manufacturing process for a semiconductor device of thepresent invention, it is desirable that the magnetic field in a dryetching step for the Cr film is a rotating magnetic field formed suchthat a combination of two orthogonal magnetic fields are applied insynchronism with each other in parallel to a surface of the correctedphotomask and adjustment of a strength of the magnetic field is effectedby controlling the two magnetic fields independently of each other.

[0032] By adjusting the two magnetic fields independently of each other,the center of the rotating magnetic field can be migrated along asurface of the photomask. Hence, when optical distortion occurs in oneside portion of the photomask or in the like case, the above describedconstitution is preferable in correcting such a kind of opticaldistortion. Moreover, this can applies to cancellation of opticaldistortion whose degree changes along a concentric circle.

[0033] In the manufacturing process of a semiconductor device of thepresent invention, it is also allowed that the second step includes aphotomask manufacturing process and a pattern on the corrected photomaskis corrected in terms of size by combining factors for a change in sizeof a pattern in at least two steps among a resist writing step, a resistdeveloping step and a Cr film etching step of the photomaskmanufacturing process.

[0034] As described above, a size of a pattern in each of regions canincrease or decease with a larger adjustment width by combining at leasttwo steps. Hence, as high degree an optical distortion as not to beadjustable in a single step of an exposure apparatus can be adjustedwith simplicity and convenience.

[0035] A photomask of the present invention is a photomask having apattern thereon, employed in transfer of the pattern onto asemiconductor wafer by means of an exposure apparatus. Correction of asize of a pattern on the photomask is performed such that correction iseffected on a variation in reduction rate of a transferred pattern ineach of regions caused by optical distortion of the exposure apparatus.

[0036] This photomask is a corrected one described above and thephotomask can be fabricated with simplicity and convenience. Sinceoptical distortion on a pattern on the photomask is corrected in termsof size, a transferred pattern with an as-intended size can be obtainedin each of regions thereof.

[0037] In the photomask of the present invention, a reduction rate canbe regarded to be one as measured in each of the regions of atransferred pattern from a fundamental pattern formed on a referencephotomask exclusively used in measurement of optical distortion of anexposure apparatus.

[0038] Since optical distortion is measured as a size of each ofregions, the optical distortion can be evaluated with much of simplicityand convenience and a method for reflecting the measured opticaldistortion on fabrication of a corrected photomask is also very simpleand convenient. Therefore, a tremendous number of photomasks required ina manufacturing process for a semiconductor device can be replaced onlywith a necessary number of corrected ones in a simple and convenientmanner. As a result, for example, a semiconductor device having a memorycapacity larger than a currently available one by one rank can bemanufactured using currently existing facilities with none of anadditional large investment thereon.

[0039] A manufacturing apparatus for a semiconductor device providedwith a photomask of the present invention is a manufacturing apparatusfor a semiconductor apparatus to transfer a pattern arranged on aphotomask onto a semiconductor wafer to perform exposure. In themanufacturing apparatus for a semiconductor device, the photomask isdisposed between a light source for exposure and the semiconductorwafer.

[0040] By employing the above described manufacturing apparatus for asemiconductor device, a high reliability semiconductor device can beprovided with a high yield.

[0041] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a diagram representing an exposure step in amanufacturing process for a semiconductor device of a first embodimentof the present invention;

[0043]FIG. 2 is a plan view representing an example pattern on aphotomask in a manufacturing process for a semiconductor device of thefirst embodiment;

[0044]FIG. 3 is a plan view representing another example pattern on aphotomask in a manufacturing process of a semiconductor device of thefirst embodiment;

[0045]FIG. 4 is a plan view representing an example unit pattern as akind of fundamental pattern on a reference photomask for measurement ofoptical distortion of an exposure apparatus;

[0046]FIG. 5 is a plan view representing a state where the unit patternson the reference photomask shown in FIG. 4 are transferred onto asemiconductor wafer by a stepper;

[0047]FIG. 6 is a diagram representing a distribution of a reductionrate shown in Table 1;

[0048]FIG. 7 is a sectional view representing a state of a photomaskhaving a synthetic quartz substrate on which a Cr film is vapordeposited and then coated with a photoresist in a manufacturing processflow for a photomask in a second embodiment of the present invention;

[0049]FIG. 8 is a sectional view representing a state of a photomask,over a resist on which EB irradiation has been performed following thestage of FIG. 1, and in the resist on which a writing section is formed;

[0050]FIG. 9 is a sectional view representing a state of the photomask,from the resist on which the writing section has been removed followingthe stage of FIG. 8;

[0051]FIG. 10 is a sectional view representing a state of the photomask,a Cr film on which has been etched off with the resist as a maskfollowing the stage of FIG. 9;

[0052]FIG. 11 is a sectional view representing a state of the photomask,the resist on which is removed following the stage of FIG. 10;

[0053]FIG. 12 is a view describing a step in which a dose has adistribution in EB writing in the second embodiment of the presentinvention;

[0054]FIG. 13 is a sectional view of a state of the photomask completedthrough a developing step and an etching step, following the state ofFIG. 12;

[0055]FIG. 14 is a view describing a step in which an exposure processis performed using the photomask shown in FIG. 13;

[0056]FIG. 15 is a view describing a step in which a beam diameter has adistribution in EB writing in a third embodiment of the presentinvention;

[0057]FIG. 16 is a sectional view of a state of the photomask completedthrough a developing step and an etching step, following the stage ofFIG. 15;

[0058]FIG. 17A is a view of a step of supplying a developer, FIG. 17B isa view of a step in stoppage of supply of the developer to allow adeveloping reaction to proceed, FIG. 17C is a step of supplying a rinseliquid and FIG. 17D is a step in stoppage of supply of the rinse liquid,all being included in the fourth embodiment of the present invention;

[0059]FIG. 18 is a sectional view describing a state of a photomaskafter EB writing is over in the fourth embodiment of the presentinvention;

[0060]FIG. 19 is a view describing a state in which a developer issupplied from a movable nozzle located in the central region of aphotomask;

[0061]FIG. 20 is a view describing a state in which a developer issupplied from a movable nozzle located in the peripheral region of thephotomask;

[0062]FIG. 21 is a view describing a state in which a etching liquid issupplied from a movable nozzle located in the central region of aphotomask in a fifth embodiment of the present invention;

[0063]FIG. 22 is a view describing a state in which a etching liquid issupplied from a movable nozzle located in the peripheral region of thephotomask in the fifth embodiment;

[0064]FIG. 23 is a view describing a state of etching in a case where amagnetic field strength is low in magnetic-enhanced dry etching of asixth embodiment of the present invention;

[0065]FIG. 24 is a view describing a state of etching in a case where amagnetic field strength is higher than that of FIG. 23 inmagnetic-enhanced dry etching of the sixth embodiment;

[0066]FIG. 25 is a view describing a state of etching in a case where amagnetic field strength is higher than that of FIG. 24 inmagnetic-enhanced dry etching of the sixth embodiment;

[0067]FIG. 26 is a plan view describing dry etching applied with aplurality of magnetic fields of a seventh embodiment of the presentinvention;

[0068]FIG. 27 is a front view representing a configuration in the dryetching of FIG. 26;

[0069]FIG. 28 is a plan view representing an example photomask having aprior art uncorrected pattern; and

[0070]FIG. 29 is a plan view representing another example photomaskhaving a prior art uncorrected pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] Below, description will be given of embodiments of the presentinvention using the accompanying drawings.

[0072] [First Embodiment]

[0073] In a manufacturing process for a semiconductor device of thefirst embodiment of the present invention, description will be givenincluding a correcting process for optical distortion of an exposureapparatus. Referring to FIG. 1, in an exposure apparatus 5, light raysradiated from a light source 5a are transmitted through a photomask 3 onwhich a pattern is formed and projected onto a surface of asemiconductor wafer to make an image. A photoactive photoresist 2 isapplied on the wafer 1 in advance of exposure. When a positivephotoresist is employed, part of the photoresist 2 irradiated with lighttransmitted through a light transparent region of a pattern 3 is removedin a developing step coming later, while part of the photoresist 2 notirradiated with the light is remained. Thereby, a pattern on thephotomask is transferred on the wafer as a resist pattern. The abovedescribed step is an exposure/transfer step in a manufacturing processfor a semiconductor device. Note that a light source for exposure may beof any type with which writing can be effected on the resist: forexample laser light or an electron beam.

[0074]FIG. 2 is a plan view representing an example corrected photomask3 in the first embodiment of the present invention. The mask is a maskobtained by correcting a pattern 113 a of no correction on the photomask103 shown in FIG. 28. Moreover, FIG. 3 is a plan view representinganother example corrected photomask 3 in the first embodiment of thepresent invention. The example of FIG. 3 is a mask obtained bycorrecting a pattern 113 b of no correction on the photomask 103 shownin FIG. 29. In the present invention, objects include not only a patternset 13 a composed of similar patterns in a repeated arrangement as shownin FIG. 2, but also a pattern 13 b with no repetition of pattern asshown in FIG. 3.

[0075] Next, description will be given of a manufacturing process forthe patterns on corrected photomasks shown in respective FIGS. 2 and 3.

[0076] First of all, in order to measure optical distortion of anexposure apparatus in terms of size, for example, a reference photomask23 as shown in FIG. 4 is prepared on which 9 cross patterns 24, whichare unit patterns (fundamental pattern) for use in size evaluation foran element, are arranged. Positions of the unit patterns each correspondto a point in the vicinity of the center of each of regions of thereference photomask 23. The 9 unit patterns 24 are all formed so as tobe of the same size as each other. Then, as shown in FIG. 5, the unitpatterns are projected onto a surface of a wafer and such a projectionis repeated by a stepper to transfer images of the unit pattern set ontoall the surface of the wafer. An issue to be processed with respect tooptical distortion of the exposure apparatus is a variation in size ofthe unit patterns P1 to P9 in a one exposure step. That is, the issuepoints out a variation in size of the unit patterns P1 to P9 in a onestep field of a transfer pattern set 30 in FIG. 5. By measuring anelement size on the photomask and an element size on the semiconductorwafer, the optical distortion of the exposure apparatus can bedetermined. Results of the measurement are shown in Table 1. TABLE 1Regions P1 P2 P3 P4 P5 P6 P7 P8 P9 Pattern 1.52 1.53 1.56 1.52 1.53 1.541.57 1.56 1.53 size on mask (M) Trans- 0.32 0.31 0.33 0.31 0.30 0.310.33 0.32 0.33 ferred pattern size (U) Re- 0.211 0.203 0.212 0.204 0.1960.201 0.210 0.205 0.216 duction rate (U/M)

[0077] When an exposure apparatus has no optical distortion, a patternon the photomask is to be transferred onto a surface of the wafer at a⅕×reduction rate. Due to optical distortion of the exposure apparatus,however, a reduction rate is not the same all over the surface of thephotomask; reduction rates are different between in the central regionand in the peripheral region. According to the results of Table 1, it isseen that the patterns in the peripheral region are transferred onto thewafer with a size larger than that in the central region. That is, theexposure apparatus has a characteristic that patterns in the peripheralregion of a mask are transferred onto a wafer with a size larger or at areduction rate larger than that in the central region.

[0078] In FIG. 6, shown is a result of plotting of the reduction rate ofTable 1 in regions. While optical distortion occurs at the same levelalong a concentric circle with an optical axis of the mask as a center,changing radially; in FIG. 6 as well, the same values of a reductionrate are located along a concentric circle and optical distortionchanges radially while keeping values equal to each other along aconcentric circle.

[0079] Corrected photomasks shown in FIGS. 2 and 3 can be obtained inthe following way: Note that for convenience of description, regions inwhich the unit patterns P1 to P9, respectively, are located areindicated by symbols P1 to P9 of the respective unit patterns P1 to P9.

[0080] Describing of the corrected photomask of FIG. 2, the patterns aof the same size of FIG. 28 are rewritten in proportion to a reciprocalof a reduction rate shown in FIG. 6. That is, a smaller pattern size alis adopted in the peripheral regions P1, P3, P7 and P9 in which apattern is harder to be shrunk in transfer when compared with the otherregions, while contrary to this, a larger pattern size a₃ is adopted inthe central region P5 in which a pattern is shrunk at a degree largerthan in the other regions. A pattern size a₂ is adopted in theintermediate regions P2, P4, P6 and P8. With such a procedure, patterncorrection rates a₃/a (for the central region), a₁/a (for the peripheralregion) and a₂/a (for the intermediate region) can be obtained in therespective regions of FIG. 2.

[0081] A corrected photomask shown in FIG. 3 is that obtained byrewriting the pattern shown in FIG. 29 such that a size L in each regionof FIG. 29 is changed in proportion to a reciprocal of a correspondingreduction rate. That is, a size L₁ of the peripheral region is setsmaller than that of the other regions, a size L₃ of the peripheralregion is set larger than that of the other regions and a size L₂ of theintermediate region is set as an intermediate value therebetween.

[0082] By use of the corrected photomasks of FIGS. 2 and 3 obtained bycorrecting with respect to optical distortion in transferring patternsonto a wafer, corrected transferred patterns are obtained and in turn,patterns with as-intended sizes specific to respective regions can betransferred. As a result, a corrected reduction rate, that is a rate insize between a corrected transferred pattern and a pattern on aphotomask prior to the correction, assumes the same values, regardlessof a region, throughout all the regions.

[0083] In the above description, description is given of the case wherea pattern is transferred larger as the pattern is located closer to theperipheral region. However, there is no specific limitation to thistendency with respect to optical distortion of an exposure apparatus,but a pattern is transferred larger either in the central region or in aspecific side of the peripheral region; an optical distortioncharacteristic alters in various ways according to an exposureapparatus. The present invention makes it possible that a pattern imageof a uniform size can be, in any case, transferred onto a wafer by useof a photomask corrected according to the characteristic of opticaldistortion of a particular exposure apparatus.

[0084] In the mean time, a measuring method for optical distortion isdescribed above with patterns on a photomask arranged such that onecross pattern is located in each region which is one of 9 regionsobtained by dividing a photomask into 9 pieces for convenience ofdescription. It is naturally needless to say that there is no specificlimitation to this way to divide the photomask into the 9 regions. Bydividing the photomask into more regions each with a smaller area,accuracy of correction can be enhanced.

[0085] When optical distortion of an exposure apparatus, that is adistribution of a reduction rate of a cross pattern, is measured and apattern is formed on a photomask such that a size thereof is inverseproportion to a reduction rate, then a transferred pattern set each witha uniform size as intended can be obtained. As a result,microfabrication of a semiconductor device can be realized in a simpleand convenient manner without installing facilities of a immensely greatcost.

[0086] [Second Embodiment]

[0087] In the second embodiment of the present invention, descriptionwill be given of a manufacturing process for a photomask corrected withrespect to optical distortion, for use in the above describedmanufacturing process for a semiconductor device.

[0088] First of all, description is directed to a manufacturing processfor a photomask used in a manufacturing process for a semiconductordevice. As shown in FIG. 7, in a first stage, a Cr film 32 is vapordeposited onto a synthetic quartz substrate 31 as a base of a photomaskand then, an EB resist 33, for example a positive resist ZEP-7000 (aregistered trade mark) made by Nihon Zeon K.K., is spin-coated thereonto a desired thickness of about 400 nm. Thereafter, the photoresist coatis baked at 190° C. for one min. Following the baking step, writing isperformed by an EB (Electron Beam) writing apparatus (not shown) to forma writing section 33 q, which is a portion irradiated with EB.Thereafter, when a pattern image in the photoresist 33 is developed by adeveloper, the writing section 33 q is selectively removed to formresist-lacking sections 33 c and 33 e as shown in FIG. 9. The Cr film 32is partially etched off based on the resist pattern to complete aphotomask. When wet etching is adopted in the etching step, the etchingliquid is sprayed. On the other hand, when dry etching is adopted in theetching step, the Cr film is partially etched off using amagnetic-enhanced dry etching apparatus as an example. By the etchingstep, Cr film-lacking sections 32 c and 32 e are formed as shown in FIG.10. Thereafter, the resist is removed as shown in FIG. 11 to complete aphotomask 3 composed of the synthetic quartz substrate 31 and the Crfilm 32 with the film-lacking sections.

[0089] A photomask having a pattern size distribution to correct opticaldistortion of an exposure apparatus as shown in the first embodiment isfabricated by means of the following process in the second embodiment.

[0090] When writing on a mask is performed by means of an EB writingapparatus, a size of a writing site alters according to a dose, which isan irradiation amount of an electron beam. When a positive resist isemployed, a size of the writing section 33 q increases in proportion toa dose and over-processing occurs with an excessive dose irradiated.

[0091]FIG. 12 is a view representing a manufacturing process for aphotomask to be corrected with respect to optical distortion having acharacteristic that a transfer size is smaller in the central region butlarger in the peripheral region as shown in Table 1. In FIG. 12, a doseof EB is more in the central region of a photomask but less in theperipheral region. As a result, a writing section 33 q is larger in thecentral region, but smaller in the peripheral region. When themanufacturing process for a photomask as shown in FIGS. 7 to 12 isapplied to a resist 33 having such a writing section distribution, thena photomask 3 having a pattern shown in FIG. 13 can be obtained. In thephotomask of FIG. 13, a diameter a₃ of a Cr-lacking section 32 c in thecentral region is larger than a diameter a₁ of a Cr-lacking section 32 ein the peripheral region.

[0092] When thus corrected photomask is used in an exposure apparatushaving the measurement result of Table 1 to form a transferred pattern,then, for example, gate patterns with a uniform size a₀ as intended orthe like can be obtained in a photoresist 42 on a semiconductorsubstrate 41 as shown in FIG. 14.

[0093] [Third Embodiment]

[0094] The third embodiment of the present invention is a process forperforming correction of a pattern on a photomask in a writing stepsimilar to the second embodiment. A process shown in FIG. 15 is aprocess in which in EB writing, a beam diameter of EB with which aresist is irradiated is adjusted, for example, such that a beam diameteris larger in the central region and smaller in the peripheral region. Alarge sized writing section 33 q is formed in an irradiated portionwhere a beam diameter is larger and contrary to this, a smaller writingsection 33 q is formed in an irradiated portion where a beam diameter issmaller. Thereafter, by applying the manufacturing process for aphotomask shown in FIGS. 7 to 11, a photomask 3 shown in FIG. 16 can beobtained.

[0095] In FIG. 16, a diameter as of a Cr-lacking section 32 c in thecentral region where an EB beam diameter is larger is larger than adiameter a₁ of a Cr-lacking 32 e in the peripheral region. As a result,when the photomask shown in FIG. 16 is used in an exposure apparatushaving optical distortion as shown in Table 1, then a transferredpattern having a uniform distribution as intended can be obtained asshown in FIG. 14.

[0096] [Fourth Embodiment]

[0097] In the fourth embodiment of the present invention, descriptionwill be given of a manufacturing process for a photomask which iscorrected in a developing step with respect to optical distortion of anexposure apparatus. Detailed description will be first given of adeveloping step. FIG. 17A is a figure showing a substep in which adeveloper 35 is supplied while rotating a photoresist having a writingsection 33 q about its center and FIG. 17B is a figure showing a substepin which supply of the developer is temporarily ceased to progress adeveloping chemical reaction for t1 second. The substeps of FIGS. 17Aand 17B are major substeps. Moreover, FIG. 17C is a figure showing asubstep in which a rinse liquid 36 to remove the developer is appliedand FIG. 17D is a figure showing a substep in which supply of the rinseliquid is ceased for t2 second. In the developing step, a series of thesubsteps shown in FIGS. 17A to 17D are repeated several times.

[0098]FIG. 18 is a photomask having a resist including writing sections33 q in a stage after EB writing is over. For convenience ofdescription, it is assumed that areas of the writing sections 33 q areuniform regardless of respective locations on a resist. When indevelopment of the photomask in the state of FIG. 18, a developer nozzle37 is positioned in the central region or is directed toward the centralregion, then an unused, fresh developer is first supplied in the centralregion. Although the photomask is developed while rotating, a freshdeveloper is supplied more in the central region than in the peripheralregion; therefore, a developing reaction progresses faster in thecentral region than in the peripheral region. As a result, as shown inFIG. 19, a diameter of a resist-lacking section 33 c in the centralregion is larger than a diameter of a resist-lacking section 33 e in theperipheral region.

[0099] To the contrary, as shown in FIG. 20, when the developer nozzle37 is positioned in the peripheral region or directed toward theperipheral region, an unused, fresh developer is first supplied in theperipheral region. Since the photomask is rotated during the developingstep, the fresh developer is supplied not only in part of the peripheralregion, but all over the peripheral region of the photomask. As aresult, as shown in FIG. 20, a diameter of the resist-lacking section 33e in the peripheral region of the photomask is larger than that of theresist-lacking section 33C in the central region. While FIGS. 19 and 20described above are for the case where a movable nozzle is employed, anozzle position is unnecessary to be fixed through all the step ofdevelopment. The positions thereof shown in FIGS. 19 and 20 arealternately selected with a prescribed period at one position to obtaina desired pattern.

[0100] Moreover, it is easy to attain an idea from the above descriptionthat when a plurality of nozzles are used in the development, a supplyamount of a developer is adjusted according to regions: the centralregion and the peripheral region and thereby, a size distribution of aresist-lacking section is provided across the photomask.

[0101] When the photomask having a diameter distribution of aresist-lacking section is subjected to the following manufacturingsteps, the photomask can be obtained in a completed form having adesired size distribution of a Cr-lacking section.

[0102] [Fifth Embodiment]

[0103] In the fifth embodiment of the present invention, descriptionwill be given of a manufacturing process for a photomask having adesired size distribution in a wet etching step. That is, in the wetetching, a size distribution can be achieved on a photomask by alteringa discharge direction of and a discharge method for the etching liquid.

[0104] A case is considered of, for example, etching of a photomask onwhich uniformly sized resist-lacking sections are distributed forconvenience of description. As shown in FIG. 21, even when uniformlysized resist-lacking sections are distributed, a size of a Crfilm-lacking section 32 c in the central region is larger than that of aCr film-lacking section 32 e in the peripheral region when an etchingliquid nozzle 47 is positioned in the central region or directed towardthe central region.

[0105] To the contrary, as shown in FIG. 22, when the etching liquidnozzle 47 is positioned in the peripheral region or directed toward theperipheral region, an unused, fresh developer is first supplied in theperipheral region. Since the photomask is rotated during the developingsite, the fresh developer is supplied not only in part of the peripheralregion, but also all over the peripheral region of the photomask. As aresult, as shown in FIG. 22, a diameter of a Cr film-lacking section 32e in the peripheral region of the photomask is larger than that of a Crfilm-lacking section 32 c in the central region.

[0106] Similar to the developing step, there is no need to fixedly keepa nozzle position through all the step of the etching. The positionsthereof shown in FIGS. 21 and 22 are alternately selected with aprescribed period at one position to obtain a desired pattern.

[0107] Moreover, it is easy to attain an idea from the above descriptionthat when a plurality of nozzles are used in the etching, a supplyamount of an etching liquid is adjusted according to regions: thecentral region and the peripheral region and thereby, a desired sizedistribution of a Cr film-lacking section is provided across thephotomask.

[0108] When the photomask having a size distribution of a Crfilm-lacking section is employed, a transferred pattern having a desiredsize distribution including that of uniform sizes can be obtained on asemiconductor wafer.

[0109] [Sixth Embodiment]

[0110] In the sixth embodiment of the present invention, a photomaskhaving a desired size distribution can be obtained by control of aplasma by a magnetic field in dry etching.

[0111] It is assumed that resist-lacking sections have a distribution ofuniform sizes for the sake of convenience of description. When amagnetic-enhanced dry etching is applied and a magnetic flux density Bis low as shown in FIG. 23, that is when a magnetic field strength isweak, then a plasma flow constituted of a etching gas is supplied morein the peripheral region and a Cr film-lacking section 32 e in theperipheral region is larger compared with a Cr film-lacking section 32 cin the central region. As a magnetic field strength increases, sizes ofCr film-lacking sections in the central region and peripheral region arealmost equal to each other as shown in FIG. 24. As a magnetic fieldstrength increases further, a size distribution can be obtained in whicha Cr-lacking section in the peripheral region is larger compared withthat in the central region.

[0112] As described above, even when resist-lacking sections have a sizedistribution of uniform sizes, a photomask on which a desired sizedistribution of a Cr-lacking section is formed can be obtained byadjusting a strength of an applied magnetic field in plasma gas dryetching.

[0113] [Seventh Embodiment]

[0114] In the seventh embodiment of the present invention, a pluralityof magnetic fields are applied in parallel to a photomask surface tocontrol a plasma gas flow in dry etching. In FIGS. 26 and 27, coils 51 xand 52 x are arranged such that magnetic fields which have equalstrengths to each other in X directions with opposed senses are appliedon the photomask, acting from both sides thereof and furthermore, coils51 y and 52 y are arranged such that magnetic fields work on thephotomask in Y direction similar to the case of X direction. There isestablished a relation of Bx=B_(1 sin θ)and By−B_(2 cos θ), and Bx andBy generate a rotating magnetic field with a direction of rotation 57 onthe photomask in synchronism between Bx and By, between the X directionmagnetic field and the Y direction magnetic field. While a center 55 ofthe composite magnetic field is located at the center of the photomaskwhen B₁ and B₂ are equal in magnitude, by altering magnitudes of B₁ andB₂ relatively, the center can be shifted, for example, along a direction56. As a result, when optical distortion does not exist at the samelevel along a concentric circle and an optical distortion alters with agradient in a prescribed direction, a size distribution of a Crfilm-lacking section which can correct such optical distortion can beprovided with simplicity and convenience. As a result, by alteringmagnetic field strengths on a pattern independently using respectivemagnetic field generators, a photomask can be obtained which correctsany type of optical distortion.

[0115] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A manufacturing process for a semiconductordevice including a step of transferring a pattern on a photomask onto asemiconductor wafer by means of an exposure apparatus, regarding opticaldistortion of said exposure apparatus as a variation in reduction rateof a transferred pattern in each of regions of a photomask, including: afirst step of transferring a fundamental pattern formed on a referencephotomask for measuring the optical distortion to measure a size of saidtransferred pattern in a corresponding one of regions; and a second stepof, based on a result obtained in said first step, forming a correctedphotomask having a pattern corrected in said corresponding one ofregions with respect to said optical distortion.
 2. The manufacturingprocess for a semiconductor device according to claim 1, wherein afundamental pattern on said reference photomask is a plurality of unitpatterns of the same shape arranged on the reference photomask.
 3. Themanufacturing process for a semiconductor device according to claim 1,wherein a fundamental pattern on said reference mask is a non-periodicalpattern with no periodicity formed on the reference photomask.
 4. Themanufacturing process for a semiconductor device according to claim 1,wherein said first step includes: a step of obtaining a reduction ratewhich is a rate between a size of said transferred fundamental patternand a size of said fundamental pattern on said reference photomask ineach of regions of said reference photomask.
 5. The manufacturingprocess for a semiconductor device according to claim 4, wherein, insaid second step, a size of a pattern in each of said regions of saidcorrected photomask is formed such that a corrected reduction rate whichis a rate between a size of a corrected, transferred pattern that is atransferred pattern of a pattern of said corrected photomask and a sizeof a pattern on said photomask prior to the correction in each of theregions is the same throughout all said regions regardless of eachlocality
 6. The manufacturing process for a semiconductor deviceaccording to claim 5, wherein, in said second step, a size of a patternin each of said regions of said corrected photomask is formed such thata product of a pattern correction rate which is a rate between a size ofa pattern in a region on said corrected photomask and a size of apattern in a corresponding region of said photomask prior to thecorrection, and a reduction rate in said region is the same regardlessof which of all said regions said region belongs to.
 7. Themanufacturing process for a semiconductor device according to claim 4,wherein, in said second step, a pattern of a prescribed portion of saidsemiconductor device is arranged in each of said regions of saidcorrected photomask in a similar way, and a size of a pattern in each ofsaid regions of said prescribed portion of said semiconductor device isdetermined such that a product of a size of a pattern of said prescribedportion of said semiconductor device in a region on the correctedphotomask and a reduction rate in said region is the same all over saidregions regardless of which of all said regions said region belongs to.8. The manufacturing process for a semiconductor device according toclaim 1, wherein said second step includes: a photomask manufacturingprocess and a pattern of said corrected photomask is corrected in termsof size by adjusting at least one of a writing beam diameter and awriting dose with respect to a position of said corrected photomask in aresist writing step of the photomask manufacturing process.
 9. Themanufacturing process for a semiconductor device according to claim 1,wherein said second step includes: a photomask manufacturing process anda pattern on said corrected photomask is corrected in terms of a size byadjusting a way of supply of a developer in a resist developing step ofthe photomask manufacturing process.
 10. The manufacturing process for asemiconductor device according to claim 1, wherein said second stepincludes a photomask manufacturing process and a pattern on saidcorrected photomask is corrected in terms of size by adjusting a way ofsupply of an etching liquid in a wet etching step for a Cr film in thephotomask manufacturing process.
 11. The manufacturing process for asemiconductor device according to claim 1, wherein said second stepincludes: a photomask manufacturing process and a pattern of saidcorrected photomask is corrected in terms of size by adjusting astrength of a magnetic field in a dry etching step for a Cr film of thephotomask manufacturing process.
 12. The manufacturing process for asemiconductor device according to claim 11, wherein said magnetic fieldin a dry etching step for said Cr film is a rotating magnetic fieldformed such that a combination of two orthogonal magnetic fields areapplied in synchronism with each other in parallel to a surface of saidcorrected photomask and adjustment of a strength of said magnetic fieldis effected by controlling said two magnetic fields independently ofeach other.
 13. The manufacturing process for a semiconductor deviceaccording to claim 1, wherein said second step includes: a photomaskmanufacturing process and a pattern on said corrected photomask iscorrected in terms of size by combining factors for a change in size ofa pattern in at least two steps among a resist writing step, a resistdeveloping step and a Cr film etching step of the photomaskmanufacturing process.
 14. A photomask is a photomask having a patternthereon, employed in transfer of said pattern onto a semiconductor waferby means of an exposure apparatus, wherein, correction of a size of apattern on said photomask is performed such that correction is effectedon a variation in reduction rate of a transferred pattern in each ofregions caused by optical distortion of said exposure apparatus.
 15. Aphotomask according to claim 14, wherein said reduction rate is one asmeasured in each of said regions of a transferred pattern from afundamental pattern formed on a reference photomask exclusively used inmeasurement of optical distortion of an exposure apparatus.
 16. Amanufacturing apparatus for a semiconductor device to transfer a patternarranged on a photomask onto a semiconductor wafer to perform exposure,wherein a photomask according to claim 14 is disposed between a lightsource for said exposure and said semiconductor wafer.